Composite compacts comprising boron carbide are used for ballistic armour and wear-resistant components. A major advantage of boron carbide is that it is extremely hard and has low density, making it the best known material for use in body armour. Consequently, boron carbide-based body armour represents the state of the art. The stopping of ballistic projectiles by a ceramic-based material is a complex, dynamic and poorly understood process. Nevertheless, it is believed that hardness and compressive strength are important properties of materials suitable for this purpose and that the strength of the material should exceed about 200 MPa. The fracture and erosion of the projectile by the armour system before it penetrates deeply into the armour material is thought to increase its effectiveness in defeating the projectile. The presence of porosity and/or soft phases are believed to deleteriously affect the performance of ceramic composite armour, as well as the performance of tools for machining, cutting, drilling or degrading hard or abrasive bodies.
U.S. Pat. No. 6,862,970 discloses a method for producing a composite boron carbide material by a reaction-bonding process that features a significant fraction of boron carbide. A molten infiltrant containing silicon and one or more sources of boron is contacted to a porous mass that contains at least some boron carbide, and also containing at least some free carbon. The molten infiltrant infiltrates the porous mass without a pressure or vacuum assist to form a composite body of near theoretical density. The silicon component of the infiltrant reacts with the free carbon in the porous mass to form in-situ silicon carbide as a matrix phase. Further, the tendency of the molten silicon to react with the boron carbide component can be suppressed or at least greatly attenuated by the alloying or doping of the silicon with the boron source. The resulting composite body thus comprises boron carbide dispersed or distributed throughout the silicon carbide matrix. Typically, some residual, unreacted infiltrant phase containing silicon and boron is also present and similarly distributed or interspersed throughout the matrix.
PCT publication number WO2005079207 discloses a composite material comprising a matrix component comprising an alloy comprising silicon having dissolved therein at least one substance comprising boron and at least one substance comprising carbon and a reinforcement component comprising boron carbide, said reinforcement phase distributed throughout said matrix, said boron carbide being substantially unaffected by said alloy. The composite material is produced by a process comprising providing a molten infiltrant comprising silicon having dissolved therein boron and carbon, and infiltrating molten infiltrant into a porous mass comprising boron carbide.
An article published in 2006 (Abramshe, R, (2006), “Improving Ceramic Armor Performance with Better Materials”, Ceramic Industry, October issue, published by BNP Media, Troy, Mich., USA) disclosed that ceramic materials that offer ballistic protection such as boron carbide, silicon carbide, silicon nitride, and mixtures of boron and silicon carbide can be improved and that new composites with a harder material, like synthetic diamond, have been developed that increase the hardness and fracture toughness of the armor plate without adding too much additional weight. Ceramic boron carbide pieces produced by means of ultra-high pressure and temperature with an outer cover of diamond is disclosed. The purpose of the diamond outer cover, which is completely bonded to the boron carbide powder in a solid piece, is to erode completely the tip of all types of projectiles before the projectile has a chance to invade the boron carbide portion of the armor plate. Eroding the projectile increases its dwell time, thereby permitting the comminuting of the entire projectile. Because the surface energies of the two species of materials are very similar, high-temperature/high-pressure, hot pressing or reaction bonding can be achieved with a small increase in cost (mainly due to the cost of the synthetic diamond).
PCT publication number WO90/09361 discloses a diamond composite comprising diamond particles bound together in a matrix of an oxide or non-oxide ceramic other than silicon carbide wherein the diamond particles comprise less than 70 volume percent of the composite. The composites of the present invention may be formed by techniques such as hot pressing, hot isostatic pressing or pressureless sintering. A disclosed method of forming the compositions involves taking an intimate mixture of diamond particles and a powder of an oxide or non-oxide ceramic, compacting the mixture and densifying/sintering it in a reducing environment at temperatures below 1,750 degrees centigrade and pressures not exceeding 200 MPa. Composites containing between 20 percent and 40 percent diamond particles by volume appear to exhibit optimum properties. Examples of non-oxide ceramics include silicon nitride, aluminum nitride, chromium carbide, titanium diboride, boron carbide and boron nitride. Twelve examples are disclosed. Each composite sample was subjected to X-ray diffraction in order to determine the extent to which the diamond particles had transformed to graphite if at all. The result of this measurement was reported in example 12, where the resulting composite as determined by X-ray diffraction was a dense material containing chromium carbide, graphite, and diamond.
GB patent number 1 595 517 discloses a process for the manufacture of hard wear resistant metal bodies comprises admixing metal powder, a powdered broronising agent consisting of boron and/or boron carbide and/or titanium boride in an amount of up to 25 percent by weight of the metal powder, and a powdered boronising activator in an amount of up to 30 percent by weight of boronising agent, placing the mixture in a mould, compacting the mixture to a density of at least a percentage of the theoretical value, and sintering the body so formed at temperatures of 700 degrees centigrade to 1,300 degrees centigrade under a protective atmosphere. An embodiment is disclosed wherein metal powders, such as cobalt or nickel, for example, can have even harder abrasive particles of material such as diamond and/or cubic boron nitride embedded therein, before and/or after the metal powder is boronised. This enables cutting tools for very hard materials to be obtained. Thus, a metal bonded abrasive body may be manufactured by the process of the invention, with diamond or cubic boron nitride abrasive particles held in a metal bonding matrix, the metal bonding matrix consisting of cobalt, present in an amount of at least 50 percent by weight and substantially uniformly distributed through the matrix, and the metal bonding matrix may consist substantially only of cobalt and boron in the form of cobalt borides, wherein the boron is present in an amount of 0.5 to 3 percent by weight of the matrix and wherein the abrasive particle content of the body is 5 to 15 percent by volume of the body.
United State patent publication number 2006/280638 discloses an intermetallic bonded composite, wherein the ceramic carbide is selected from a group consisting of titanium carbide (TiC), silicon carbide (SiC), tungsten carbide (WC), and boron carbide. The composite is formed by a process of milling the high-temperature intermetallic binder and diamond particles, pressing the high-temperature intermetallic binder and diamond particles, and, sintering the high-temperature intermetallic binder and diamond particles to form the intermetallic-bonded diamond composite, wherein the high-temperature intermetallic binder comprises an alloy having a processing temperature of at least about 1,200 degrees centigrade.
There is an ongoing urgent need for boron carbide-based ceramic composites that have improved ballistic projectile stopping (defeating) properties, or which are suitable for cutting, machining, drilling or degrading hard or abrasive materials, but which are also cost-effective.